Apparatus for heat transfer at high temperatures



C. FIELD APPARATUS FOR HEAT TRANSFER AT HIGH TEMPERATQRES March. 1, 1927.

Filed April 17, 1922 1 :5 Sheets- -Sheet 2 [hwy field mm m 9H E m 2 m 3;: 1 l z. w a 11%? 0 $.11- M v V Y m .J a/ HM. T

I '161 ,661 March 1,1927. c. HELD 9 v APPARATUS FOR HEAT TRANSFER AT HIGH TEMPERATURES Filed April 17, 1922 5 Sheefs-$he9t 5 a 5m :t 70 a :6 J:

Crwby li'ela" B 5 M Elll bowwq Patented Mar. 1, 1927.

UNITED STATES 1,619,661 PATENT OFFICE.

CROSBY FIELD, OF YONKEBS, NEW YORK, ASSIGNOR TOCHEMICAL MACHINERY GOR- PORATION, A CORPORATION OF NEW YORK,

APPARATUS ron HEAT rmivsrnn AT HIGH ramrnnarumis.

Application filed April 17, 1922. Serial No. 553,640.

My present invention is more or less closely related to certain heat transferring operations of the classes described in my prior application, Serial Number 141,949, filed January 12th, 1917, Patent No. 1,403,471, granted January 10, 1922. In the present case the heat transferring medium is a liquid of boiling point much above that of Water, perferably mercury; the temperatures at which heat is to be transferred are usually. far above said boiling point of water; the temperatures of heat transfer either to the transferring medium or from the transferring medium, or both, are determined by the internal pressures at the boiling or the con densing points, or both; and these pressures may be 'controlled either by hand manipulation or automatic action of valves, pumps or otherqsuitable pressure controlling devices.

My present invention includes regulating the temperature in. the heat transferring system by controlling the internal pressure by and in accordance with the temperature of a region or substance to be heated or cooled; or by the difference between the internal and external pressures; and the external pressure may be atmosphere or may be one maintained in an auxiliary part of the system by a vacuumizing or other pressure controlling pump.

In the preferred embodiment and in nor mal operation the pressure is approximately uniform throughout the circuit of the heat transfer medium, although the pressure at the boiling or heat absorption point may be higher than at the condensing or heat yielding point.

While the system maybe employed partly or exclusively for cooling, the primary pur-v pose illustrated is heating substances, for

distillation, sublimation or chemical reactionwhich require limiting the temperatures for a predetermined maximum or minimum, or between a maximum and a minimum; or for different temperatures successively.

My present invention includes systems wherein there is 'a supplemental condenser located beyond the primary condensing region and adapted to return its condensate to the circulating system. In certain cases the supplemental condenser is beyond the pressure controlling valve; in others it is between the primary condensation or heat yielding region and the pressure controlling valve; in others between the pressure conadapted to withdraw foreign gases and im-- purities from the circulation and these are preferably arranged to discharge the impurities into the atmosphere without interfering with return of condensate to the circulation and without interfering with the desired vacuum or pressure conditions within said circulating system.

In certain cases the desired operation is continuously endothermic or heat absorbing. In such case the heatin is by the condensation portion of the cycIe and the control of temperature is accomplished entirely by control of the pressure of the vapor being con-- densed.

An important feature of my invention,

however, concerns a system which will a'utomatically control the temperature of a desired region when the operation in said region requires heating at one time and cooling at another time under conditions where the operation of the fluid medium must shift from a primary condition of condensing to impart heat, over to a, secondary condition of boiling" to absorb heat; and to do this automatically. This very diflicult special case is frequently met with in the chemical industry. Certain chemicals in the mixture must be heated to a predetermined critical temperature. In certain cases, notably oxidation or partial oxidation of organic compounds, heating to a certain critical tem-ff perature will initiate an exothermic or heat evolving reaction. The heat thus evolved, necessarily raises the temperature further c, and the higher temperature thus produced may cause a decomposition of the product or even an explosion and in most cases it will create a condition unsuitable forj the best performance of the desired reaction. Hence one part of my invention concerns maintaim ing a body of liquid medium in heat absorbing relation to the same regionwhich is iniios tially heated by condensation of the heated operations will come into eflfect successively and automatically upon change of a few degrees in the temperature of a chemical mixture, even without change of the internal pressures. Moreover, where there is automatic, thermostatic control of pressures by and in accordance with the heat of the chemicals, as above mentioned, the regulation may be even closer.

The above and other features of my invention will be more evident from the fol lowing description in connection with the accompanying drawings, in which- Figs. 1, 3, 4 and 5 are diagrammatic views of systems embodying various features of my invention.

F Fig. 2 is a sectional detail on the line 22,

In these drawings the boiler, pipes, valves, condensers, and all other parts likely to contact with mercury are preferably of iron or steel, since this material is ordinarily not attacked or even wetted by mercury. The various containers and pipes for performance of the heating function are understood to be properly heat insulated.

Fig. 1 shows a system particaularly adapted for certain cases of heating operations where the operation is one of impartin heat and the substance or region to be heate does not generate heat in excess. of its own radiation losses. That is to say, the system is one for continuous or intermittent heat petroleum an usual mechanical application.

The system comprises a heat absorbing and mercury boiling element which in this case is a boiler 1, connecting through pipe 2 with a condensing or heat-imparting coil 3, in contact with a cooling medium 4 in a suitable container 5. In this case the cooling medium is usually a compound or mixture of compounds to be heated for the purpose of causing distillation or sublimation or chemical reaction or all three, either simultaneously or successively. The container 5 may be of any desired metal suitable for its purpose since the mercury does not come in contact with it. As shown it is hermetically closed by a top 6 communicating through a ipe? with a cooling chamber 8, the whole eing vacuumized through pipe ,9 by pump diagrammatically indicated at 10. Distillate or sublimate' caught in chamber 8 may be removed through a suitable outlet, as for instance, the valve controlled pipe diagrammatically indicated at 11. These parts ma be the ordinary vacuum distilling or su limating unit, such as commonly em loyed in the manufacture of coal tar roducts; and the stirring means (not shown) may be employed if desired tem er While the mercury boiling element 1 may be usefully employed as a cooling element for any desired heat evolving system, it is shown in this case as being electrically heated from any desired source of ower.

As will be evident from the drawings, the

coil 3 is a down-flow condenser and it discharges through pipe 12 from which the condensed mercury has a return flow path through pipes 13, 14 and branch pipes 15, 15, to the ends of boiler 1. Any uncondensed vapor can pass up through pipe 22 whence its furt er progress will be determined by the pressure control instrumentalities.

The internal pressure is controlled by controlling the escape of such vapor. In the present case there are two controls either of which may be employed separately but which have peculiar advantage when emplolyed in combination.

he vapor from 12 is discharged into pipe 22, from which in normal operation of the device it will be permitted to flow through certain controllin devices into pipe 23, upflow condenser C011 24, vacuumized through pipe 25, check'valve 26, pump 10 and discharge outlet 29. The jacket of condenser 24 is supplied with cooling water through pipes 24*, 24*. A trap 29 may be interposed in pipe 29 containing material adapted to combine with the last traces of mercury vapor, thus preventing any mercury from escaping to the outer air.

The suction ump 10 is utilized to maintain in the con enser 24 and pipe 23 a pressure which is usually atmospheric and which in any event is preferably less than the pressure 1n pipe 22, which latter is preferably As shown in the'drawings, the pressure relief valve 30 may be set for above-atmosphere ressures in the system as by havin the weight 30a to the right of fulcrum 30 as shown in Fig. 1; or for below-atmosphere pressures as when the weight is to the left of said fulcrum. When the predetermined pressure is exceeded the valve automatically opens and vents the vapor into pipe 23 and condenser 24. For below-atmosphere pressures the pump will be operated in the usual way. For above-atmosphere pressures essired amount of substance 4 to cape may be through pipe 27, check valve 28 and outlet 29. A check valve may be provided at 26 toprevent accidental back flow of gaseous products from the still into the mercury condenser 24.

As before mentioned, valves 16 and 30 are adapted for operation in combination as follows:

Container 5 being supplied with the debe heated, pump 10 is started vacuumizing the heating -system through pipe 25, condenser 24, pipe 23, and one of the valves 16 or 30, which may be held open for the purpose. The resistance 40 being properly adjusted, switch 41 is closed, current flows through'mercury in the container 1 and also through the walls of the container heating and eventually boiling the same. The hot vapor flows through pipe 2 and condenser coil 3. Material 4 being cold, practically all of the mercury will be condensed; also the heat sensitive element 18 will be cold, so the valve 16 will be closed.

Valve 16 will remain closed until the substance 4.is heated up to the desired critical temperature for which the device 19 is adjusted and pressure relief valve 30 will stay closed until the internal pressure exceeds that for which said valve is set. Normally then the boiling, condensing and heating may proceed until the internal pressure exceeds that for which valve 30 is set and thereafter venting through 30 will control until the mixture 4 reaches the critical temperature for which the thermostat 19 is set.

Preferably the thermostat 19 will be set to control at lower pressures than the pressure relief valve 30. Hence when the material 4 is once heated enough to bring the thermostat valve 16 into action, it will control exclusively unless or until vapor is generated in excess of the capacity of said valve 16, in which case the pressure relief valve will act as an ordinary safety valve blowing ofi at the predetermined higher pressure for which it is set.

Preferably the valve 16 is used for close regulation of below-atmosphere pressures, pipe 23 being vacuumized sothat the pressures therein will always be less than that in the circulating system. Usually valve 30 will be set for control where internal pressures above atmosphere are desired and in such case valve 16 may be permanently closed.

The liquid condensate can return through said valve 16 whenever it is open, but when- 7 ever valve 16 is closed, and valve 30 is controlling, the return of condensate will be through down opening check valve 34 and will occur whenever weight of the condensate becomes sufficient to open said valve against the. internal pressure. Other settings of one or both valves for either sep- ,of mercury in pipes 13,-

arate or conjoint control, either below or above atmospheric ressure, will be selected to suit special (Hm itions or purposes. The pressures may be predetermined by calibration of 19 and 30, but pressure gauges may also be employed as at 54 in pipe 2 or in pipe 31.

The container in which mercury is boiled to absorb heat is long as compared with its cross section and is formed with a central vapor collecting dome 40 and also with reduced ends 44, 44. The heating current is supplied through electrodes 42, 42, mounted in insulated blocks 43, 43, in said reduced ends 44. The reduced ends afford the smallest cross section and greatest heat development tends to localize therein; also the return of condensate through branch pipes 15, 15, is to these regions of greater heat development. The mass of mercury in.

boiler 1 affords a path for electric current which is of so much lower resistance than any other path that the leakage losses in other directions are minimized but insulation may be employed for parts above the level of the liquid mercury, as diagrammatically indicated at 50.

In the apparatus of Figs. 1 and 2, the level of the mercury is preferably at or near that indicated by dotted line 46, 46. This level is high up in the boiler, is well above the level of return'pipe 13, 14, and is well below the level of return pipe 12. Thus the flow of vapor and condensate through pipe 12 is free and unthrottled by any static back pressure of mercury, while the body 14, maintains a liquid seal against back flow of mercury vapor through said pipes.

he system shown in Fig. 3 resembles that of Fig. 1 in man respects but has important differences. Xnalogous elements include region 101 in which the fluid medium absorbslieat and boils, "the pipe 102 for upflow of the vapor, the gauge 139 indicating internal pressure, the worm coil 103 wherein the vapor condenses for imparting heat to the material 104, the container 105 for the latter, the pipe 112 for outlet of condensate and uncondensed vapor, the down flow pi e 113 and the return pipe 114 for return flow of the condensate to the boiler element 101, all being substantially as above described.

In the present case the boiler 101 is heated by a current from the secondary of trans-' former T, the primary of the transformer being supplied with alternating current through suitable controlling devices including the switch 141. The transformer is par-Q ticularly useful because of convenience 'in stepping down the voltage to get c0rrespondingly great amperage for heating ef feet on the boiler 101. p

The pipe 112 leads to and the pipe 113 Gil drains out of the bottom of a tubular upflow condenser 124, which in this case is between the primary or heating condenser 103, and the pressure regulating devices. The upper part of the condenser has an outlet through pipe 125 which may be vacuumized by pump 110. In place of the thermostatically controlled valve 30 of Fig. 1,.

there is a pressure relief valve 130 ad ustable for venting at the desired internal pressures, indicated by position of Weight 130 as being less than atmosphere. This valve may be set for internal pressures greater than atmosphere by shifting the weight to the other side of the fulcrum. When internal pressures above atmosphere are required, the pump may 'be cut off by valves 110, 110. Then the outlet will be through parallel pipe 127 which provides'a by-passfrom the intake 125 to the discharge 129 of pump 110. This by-pass 127 may be controlled by a pressure relief valve 130 adapted to be set for venting internal pressures above atmosphere. These valves 130 and 130 are adapted for conjoint or successive operation somewhat as described by valves 16 and 30 of Fig. 1, except that the primary valve is controlled by internal pressure instead of thermostatically.

The uncondensed gases passing either through pump 110 or the by-pass 127 flow through 129 to the residual condenser 124. The lower end of this condenser connects through a barometric U-leg 113, and pipe 113 with the return pipe 114 which leads back to the boiler 101. The level of the mercury is indicated by the dotted line 47, 47,, as being near the top of boiler 101; below the drainage pipe 112 and condensers 124, 124; but above the barometric U pipe 113, and the return flow pipes 113 and 114.

There is a pipe 129 afi'ording an atmos heric outlet from pipe 113, below the residual condenser 124, but above the level of the mercury. Outlet pipe 129 may have interposed. therein a trap 29 like the trap 29 in Fig. 1.

It will be understood that the closed circuit through the residual condenser 1 24 and the barometric U, 113, may be' used in conjunction with the system shown in Fig. 1, as may also the pipe 129 through which uncondensible gases may be discharged to the atmosphere.

In the system shown in Fig. 4, the vac uumizing pump 210, the supplemental condenser 224, residual condenser 224, the primary pressure relief valve 230, secondary relief valve 230, container 205 for the material 204. which is to be heated, as also the adjustment and methods to be performed,

. ma be substantially the same as in Fig. 3.

It 1s noted, however, that the supplemental condenser 224 is a down-flow condenser and Va or ihis arrangement whereby the pressure of the liquid mercury in the jacket does not interfere with the circulation of the condensing vapor facilitates employment of an important feature not found in Fig. 3; namely, arranging matters so that the normal level of the mercury, indicated by line 47-47, is substantially above the bottom of the container 205, so that the lower portion of said container is continuously bathed in a body of liquid mercury. In normal operation, this mercury will be hot condensate which may be at or near the tem erature of condensation as determined by t e particular internal pressure then being maintained by the pressure regulating valves. This body of condensate in the jacket is in an important strategic position in several particulars.

In case of ordinary work requiring only endothermic or heat absorbing operations on the material 204, the condensed mercury is free to flow downward through 212 and back to the boiler 201 as in Figs. 1 and 3.

But in cases where the reaction in material 204 becomes exothermic or heat generating, this mercury automatically begins to function as a cooling medium. It obsorbs heat from the container 205 and begins to boil as soon as the temperature of the mixture 204 rises slightly above the critical condensing temperature as determined by the pressure controlling devices. The boiled oif liquid is replenished through pipe 212 after the same manner as theprimary boiler 201. The vapor resulting from the boiling has a free path of escape through the regular vapor outlet 212 to condenser 224 and its pressure, condensation and return flow to the jacket or secondary boiler may be automatically controlled by the instrumentalities above described for the primary boiler. Obviously, however, the adjustment of the pressure relief valves may be changed ifit is desired to conduct the heat generating reaction at a different temperature from that which initiated it.

Moreover, where said reaction may be desirably continued at a higher temperature requiring a higher internal pressure of the mercury vapor the sudden and great increase in the total volume of vapor due to the (jacket becoming a mercury boiling instea, of a mercury condensing device may be taken advantage of to cause control to shift to a pressure relief valve set for a higher pressure and temperature than the one which controls the initial heating. In such case the sudden increase in volume of vapor may exceed the condensing capacity of the first condenser, in which case a valve,

like 230 set for a below-atmosphere pressure may be forced open continuously and if the pumping capacity of pump 210 is also exceeded valve 230 will become the pressure determining instrumentalit If the pressure control system of Fig. 1 be em loyed under conditions above describe the thermostatic valve 16 is likely to be too small to sufiiciently relieve the increasing pressure even when wide open, in which case a back pressure will be built up until the pressure relief valve 30 becomes the controlling instrumentality. In such case said valve 30 will be set for the desired exothermic reaction temperature and will come into operation automatically whenever said reaction commences.

In the system of Fig. 4, it will be noted that if the mercury level were lowered below the bottom of jacket 203 there would be no body of liquid mercury in the jacket and the entire space would be available 'for mercury vapor heating. A system better adapted for operation with the mercury above or below the bottom of the container or at any desired level is illustrated in Fig. 7.

In this figure, the boiler 501 is upright and extends from and below the lowest level of mercury indicated by line 47, 47, to a point well above the higher level indicated by 47 v47, the former line being below the bottom of the jacket 503 and the latter above the bottom of container 505. This boiler 501 forms part of a single turn secondary, circuit of which is completed through copper bar 501 which is of low enough resistance to practically short circuit the rest of the system. This single secondary is energized by primary coil 501 being controlled by switch 541.

The container 505, the jacket 503, the vapor supply tube 502, the gauge 539, the

- vapor outlet tube 512*, the down-flow tube 512 for the condensate, supplemental condenser 524, return pipes 513 and 514 may be the same as in Fig. 4. For convenience there is preferably a glass guage 555 across pipes 502514 for indicating the level of the mercury in the system. In this system, the pressure controlling valve 530 is located in the pipe 512 between the jacket 503 and the condenser 524 and, as diagrammatically indicated, it is adapted to be set for pressures either above or below atmosphere. The exhaust pump is beyond the condenser and consists of a well-known form of barometric jet condenser comprising the upwardly extending suction tube 525 for the vapor, discharging downwardly through the jet 510 in chamber 510 supplied with water through opening 510 controlled by valve- 510. This chamber connects with downwardly extending tube 529 which is long enough to afford a barometric column when water is the fluid. The pipe 529 has an outlet at 550 below the level of the liquid in container 551. This container has two water outlets, one 552 at proper level to drain oil water when the mercury level is at 47, 47,'

and the other 553, when it is at level 47, 47. The mercury vapor is condensed by the water and settles out in the container 551. It might be returned to the system through a barometric U tube like that in Fig. 3, but as shown there is a lrand operated valve at 554 which is opened only when the internal pressures are suitable for in-flow of mercury without disturbing of the adjustment of the apparatus.

In the system of Figs. 4 and 5, where a body of liquid mercury may be and preferably is maintained in contact with the lower portion of the same container which. is being heated by condensation of the mercury vapor, there is special advantage in employing a vertically arranged propeller to afford vertical circulation of the mixture, and in Fig. 7 I have shown for this purpose a screw propeller on the lower end of vertical shaft 71 journalled in the cover 506 and power driven through any suitable means, as for instance, a ear 72 driven by gear 73 on shaft horizonta 74 which is supported in a bearing 75 and may be rotated from any desired source of power diagrammatically indicated by belt pulleys 76, 77, one of which may be an idler while the other is keyed to said shaft 74. The vertical circulation thus provided is important not only for mixing but also for driving hot mixture into cooling relation with the llquid mercury for boiling the latter during exothermic reactions and also for displacing the cooler material upward in heating relation with the condensing area of the container when the operation is endothermic.

It will be understood that the presence of liquid mercury in bathing contact with the same container which is heated by condensation of hot vapor supplied from an outside source, is of great importance, not only for controlling the temperature during desired exothermic reactions, but also as an ever present refrigerating medium which will automatically come into op eration as a safety appliance in cases where undesired exothermic reactions may occur by accident as in case of certain impurities in certain mixtures or in case of faulty regulation by the pressure controlling devices.

A not uncommon case is where there is a small amount of impurity capable of oxidizing or other exothermic reaction within the range of the desired operating temperature. In such case the coolin" action of the boiling mercury will be sufiicient ito keep down the temperature until the exothermic reaction has been completed, after which the process will proceed as before. cases, as where the amount of material for the exothermic reaction is considerable, it may be necessary to have expert attendance and regulation to completely take care of the situation. Even in cases where the danger never materializes, the advantage of. the liquid mercury as a precautionary safety device is obvious.

It will be understood as to all of the systems shown herein that adjustment of heating current may be suchv as to boil mercury at rates suflicient to supply more vapor than will be condensed in the heating coil or jacket. Such excess represents waste but unless maintained the system controls will operate only as upper limit regulators. If, however, the vapor is always in excess, the working temperature will be kept up to the predetermined limit as well as prevented from falling below it.

While the various systems disclosed herein are capable of being operated either above or below atmosphere, as heretofore explained, there are great advantages in employing them for the operations which can be performed at or blow atmospheric pressure. that is, for temperatures at or below 357 centigrade, the atmospheric boiling point of mercury. Hence, as will be evident, a

great variety of heating operations, particularly for chemical reactions can be accomplished with the secondary valve, as for instance, valve 30, Fig. 1, set to blow at or below. atmosphere. In the below-atmosphere operation there can be no leaks of mercury, to the exterior. Any leaks must be inward into the system and any impurities thus introduced are drawn oil with the excess uncondensed vapor and are gradually worked out of the system by continued operation of the vacuumizing ump. While the leaks are thus in the direction of safety as regards human life and are taken care of as above highly undesirable and the greatest possible care is taken to prevent them.

-.In my prior application first above mentioned I have stated that mercury vapor may be obtained at 430 Fahrenheit under a pressure'of only nine-tenths-poun'ds to the square inch. Higher degrees of heat may be obtained with corresponding increase in pres-- sure. And I- have also described how these I pressures, required for desired temperatures,

In other can be maintained by a vacuum pump operated and controlled in the usual manner in connection with an ordinary pressure gauge. which indicates the boiler ressure. While the methods claimed in sai application can be practiced by manual control of the puinp in connection with the gauge, there are imare the various forms of vacuumizing pumps,

Such pumps require no special description or illustration, being Well-known in the art, and they may be continuously operated for predetermined low vacuum without special regulation. It will be noted, however, that in ordinary operation they are not required to maintain vacuum any greater than is necessary to give internal pressures free vent when the relief valve is open. Hence said vacuum pumps may be supplied with automatic control mechanism to maintain only the required degree of vacuum; and when the valves are set for above-atmos here pressures, the pumps may be cut oii either by hand valves as indicated in Figs. 3 and 4, or by any desired automatic mechanism.

It will be understood that the pressure relief valves, such as 30, 130, 130*, 230, 230 and 530, are diagrammatically indicated as having the internal pressure on the valve element directly opposed by external atmos-.

pheric pressure which latter is adjustably decreased or increased by the weighted lever. It will be understood. however, that I may employ separate motive means, adjustably goverened by the pressures, to do the work of moving the valves, thereby making the regulation closer and more certain.

In systems of the type herein described} transfer of a given amount of heat requires boiling and condensing of relatively large amounts of mercury. Hence the velocity of the vapor flow is great and the resulting friction may give rise to a certain amount of back pressure. Hence it will be understood as to all of the systems the mercury level in the boiler may be somewhat below that in the pipes leading from the condensers and itwill sometimes be necessary to make allowance for this;

In this same connection it may be noted that the level of the condensed mercur may be regulated to a desired higher level the mercury in the boiler by throttling of the return flow of the condensed vapor.

than

For instance, in Fig. 7 the mercury may be .boiler is at a much lower level by suitably adjusting valve 570 which can be inserted in pipe 512. The back pressure could be varied by partially closing a similar valve, which can be arranged in pipe 502. Preferably, however,- the back pressure should be kept as small as possible so that the pressure throughout the entire system may be more nearly uniform.

I claim:

1. A mercury boiling and condensing system including a mercury boiler, means for heating it, a mercury vapor condenser, conduits for flow of vapor from the boiler to thecondenser, and for return flow of condensate to the boiler, and a container for maintaining'material in heat absorbing relation to the condenser, in combination with a thermostatically controlled regulating valve insensible to pressures within the system, adapted to vent the system to limit the mercury vapor pressure and thereby regulate the temperature of the condenser and a second pressure controlled vent valve adapted to 'relieve internal pressures independently of the temperature in the condenser.

2. A mercury boiling and condensing system including a mercury boiler, means for heating it. a mercury vapor condenser, conduits for flow of vapor from the boiler to the condenser, and for return flow of condensate to the boiler, and a container for maintaining material in heat absorbing re lation to the condenser, in combination with a pressure insensible thermostatic valve,

adapted to regulate the mercury vapor pressure and thereby regulate the temperature ofthe condenser, and a heat insensible pressure operated valve adapted to open at a higher mercury vapor pressure than that normally controllable by said first-mentioned valve.

3. Amercury boiling and condensing system including a mercury boiler, means for heating it, a mercury vapor condenser, conduits' for flow of vapor from the boiler to the condenser. and for return flow of con-' densate to the boiler, and a container for maintaining material 1n heat absorblng relation to the condenser, in combination with a thermostatically controlled, regulating valve adapted to vent the system at a predetermined mercury vapor pressure and thereby determine the temperature of the condenser, and a pressure operated relief valve controlling an independent vent for the mercury vapor pressure and adapted to open at higher mercury vapor pressure than 1 that normally controlled by said first-mew tioned valve.

4. A closed circuit system i for indirect heating to high temperatures including a mercury boiler element, a mercury vapor condenser, a conduit for flow of mercury vapor from the boiler to the condenser and a closed return conduit for flow of condensate from the condenser to the boiler, a. container for maintaining the material to be heated in heat absorbing relation to the condenser, in combination with a supplemental condenser and means for cooling the-same, and an outlet from said first condenser to said supplemental condenser. I

5. The combination specified by claim 4,

with a return conduit for condensate from a connection with the outlet from the first "condenser.

7. A closed circuit system for. indirect heating to high temperatures including a n'lercury boiler element, a condenser ele- ,ment, a conduit for flow of mercury vapor from the boiler to the condenser and a closed circuit return conduit for flow of condensate from the condenser to the boiler, the condenser element including .a container for maintaining the material to be heated in heatabsorbing relation thereto, in combination with a supplemental condenser and means for cooling the same. connected with an outlet for said first condenser, a pressure operated relief valve adapted to vent internal pressures at a predetermined pressure below atmosphere and a vacuum 1 ump maintaining the system at a pressure below ork in the county of said predetermined ressure.

Signed at New New York and State of New York this 15th day of April, A. D. '1922.

- I CROSBY FIELD. 

